How  would  you  account  for  the  increasing  oxidising  power  in  series  VO₂ ⁺  <  Cr₂O₇ ^2-  <  MnO₄ ^-  ?

The oxidation state of the transition metals in the given compounds is:

The higher the magnitude of positive charge on the metal ion, greater is the oxidizing power of the metal, as the increasing order of oxidation state is +5 < +6 < +7, therefore the increasing order of the oxidizing power will be :

VO₂⁺ < Cr₂O₇^2- < MnO₄^-.